A computer assisted method was employed to estimate the amounts of cerebrospinal fluid, white matter and gray matter in individual computerized (CT) scans of brain. Imaging processing procedures including DMORPH and CATSEG were applied to CT scans. Computer assisted tomography (CT), together with three dimensional image reconstruction procedures, demonstrated in healthy men between the ages of 21 and 81 years, that the volume of cerebrospinal fluid increased in relation to age and that the volume of gray matter was correlated negatively with age, whereas the volume of white matter in the brain was age invariant. Volumes of lateral and third ventricles were elevated with advancing aging, while volumes of the thalamus and lenticular nucleus were reduced. Volumetric CT analysis showed reductions in young Down syndrome subjects, as compared to young controls, in intracranial volume and gray matter volume. However, the differences were not evidenced when the results were normalized to subject height, indicating that brain changes were proportional to height in Down syndrome. Left ventricular dilation was noted by CT analysis in brains of autistic adults. Even in healthy subjects, brain atrophy occurs with aging. The volumetric analysis technique also demonstrated brain atrophy, above and beyond that noted with respect to healthy aging, in subjects with Alzheimer's disease as well as dilatation of cerebrospinal fluid spaces. The degree of atrophy was related to psychometric scores for dementia and mental competence.